Computer chip design has improved at a rapid pace. According to Moore's law, the number of switches which can be produced on a computer chip has doubled every 18 months. Chips now can hold millions, of transistors. However, it is becoming increasingly difficult to increase the number of elements on a chip using present technologies. At the present rate, in the next few years the theoretical limit of silicon based chips will be reached. Since, the data storage and processing capabilities of microchips are determined by the number of elements which can be manufactured on a chip, new technologies are required which will allow for the development of higher performance chips.
Present chip technology is also limiting when wires need to be crossed on a chip. For the most part, the design of a computer chip is limited to two dimensions. Each time a circuit must cross another circuit, another layer must be added to the chip. This increases the cost and decreases the speed of the resulting chip.
A number of alternatives to standard silicon based complementary metal oxide semiconductor ("CMOS") devices have been proposed, including single electron transistors, quantum cellular automata, neural networks, and molecular logic devices. (Chen et al., Appl. Phys. Lett. 68:1954 (1996); Tougaw, et al, J. Appl. Phys. 75:181 (1994); Caldwell, et al., Science 277:93 (1997); Mead, Proc. IEEE 78:1629 (1990); Hopfiled, et al., Science 233:625 (1986); Aviram, et al., Chem. Phys. Lett. 29:277 (1974); and Petty et al. Eds., Introduction to Molecular Electronics (Edward Arnold, London, 1995)). The common goal is to produce logic devices on a nanometer scale. Such dimensions are more commonly associated with molecules than integrated circuits.
DNA molecules has recently been used as a support structure for the formation of 100 nanometer scale silver wires (Braun et al., "DNA-Templated Assembly and Electrode Attachment of a Conducting Silver Wire," Nature 391:775-78 (1998); PCT Application WO 99/04440, which are hereby incorporated by reference). Furthermore, the DNA molecule allows for specific targeting of the end of the DNA-wire to complimentary nucleotide sequences on a chip. The reduced size of these wires allows for a lower level of voltage to be used in a circuit, decreases operating temperatures and magnetic field strength, and faster circuits.
Integrated circuits on computer chips require numerous structures including, resistors, capacitors, and transistors. Therefore, the reduction of wiring to the 100 nanometer level may somewhat reduce the size of integrated circuits but the improvements are limited by the size of the other components.
Nucleic acid molecule directed assembly is also advantageous because it can direct the synthesis of three dimensional structures. Inductors can not be constructed on conventional chips, because they are three dimensional structures. Molecular biology provides tools for manipulating nucleic acid molecules at the molecular level. Nucleic acid molecules also provide other advantages, since nucleic acid molecules can be rapidly replicated with high fidelity using existing technologies. Furthermore, nucleic acid molecules can store information in their structure which can be used to direct the formation of complex circuits.
"DNA computers" have also been described recently in the literature in which computation occurs via chemical reactions. (Adelman, Science 266:1021 (1994), which is hereby incorporated by reference). This method has limited usefulness, because the nucleic acid molecules must be synthesized, reacted together, and the appropriate "result" must be isolated and sequenced. Thus, it is unclear how this technology could be used for everyday applications.
Therefore, new methods of fabricating integrated circuit components are needed, where elements of an integrated circuit can be manufactured on a nano scale. Furthermore, a need exists for taking advantage of the information coding capabilities of DNA in the formation of integrated circuits.